There's a trigger on the Genuine Inovations Pump/CO2. In order to save CO2, I use mine in pump mode just to get some air into the tube, and to make sure the tyre is seated correctly, without any pinching. When I'm happy with the seating and position of the tyre, one 16oz cartridge is sufficient to get a 700x23 up to around 110psi. On my MTB a 26x2" tyre needs 3 CO2 cartridges to get it up to 85psi; a 26x1.5" tyre needs around 2 cartridges; so the lesson here is to always take more than one cartridge. YMMV…
- Wil